For many years grain has been carried in boxcars and for this purpose it is necessary to install temporary barriers across the boxcar doorways. It is apparent that if only the sliding stormdoors are utilized, the grain can leak out as soon as it is introduced. Therefore, the practice has long been followed of coopering a temporary door across the inside of the door posts. A preferred form of door incorporates horizontally extending metal straps which are nailed or otherwise anchored into the door posts and used as a basic support for a relatively stiff paperboard sheet -- such as a corrugated paperboard. The sheet, or panel of paperboard necessarily must be wider than the doorway itself so as to prevent leakage along the sides, and hence the edge portions of the door panel have been equipped with fold lines -- so as to develop side flaps exposing the metal straps for nailing into the door posts. After the nailing has been complete, the flaps are "unfolded" or positioned in generally planar relation with the rest of the door panel -- such a construction being seen in U.S. Pat. No. 2,966,438.
In the past, the nailing operation (more particularly, the management of the side flaps) was onerous. When it is considered that there is a great deal of resiliency to the paperboard door, it can be appreciated that the artisan doing the nailing (or coopering) has had to fight the tendency of the side flap to spring back into its original position. Sometimes this has been solved by using two artisans -- one holding the flap while the other does the nailing. On other occasions, the artisan would use a wire to hold the flap in its "fold back" condition. Any rough handling of the door, including the side flaps, can result in damage which could result to leakage of grain. The presence of grain external to the temporary door, i.e., on the sill of the boxcar, raises a suspicion in the mind of the recipient, or buyer -- just how much has been lost? Therefore, it is highly desirable to make sure that the seal effected by the grain door is perfect.
Through the instant invention, I have solved both of these problems, alternatively, have provided two advantages through the provision of a single novel structure. The introduction of upwardly and downwardly diagonal fold lines from the intersection of the horizontal floor flap fold line and the vertical side flap fold line makes it possible for one artisan to conveniently fold the side flap back and without the need for applying any damage-inducing stresses.
Other advantages of the invention may be seen in the ensuing detailed description.